Many projectors used to project an image on a screen, such as, for example, in a classroom setting or the like, are provided with a single lens that projects images having a predetermined particular throw ratio. The throw ratio for a projector is a defined as the ratio between the distance between the projector and the screen and the width of the image projected. Where a projector is provided with a zoom lens, the modification of the throw ratio is relatively simple. However, zoom lenses and their associated structures are relatively expensive and when not properly cared for or operated, can become a maintenance problem. Accordingly, there is a need for a structure that permits the inexpensive and reliable modification of the throw ratio of a projector.